Multidisciplinary approach to revisit the state of activity of a deep-seated gravitational slope deformation in the frame of the Quaternary geomorphological evolution of the Central Apennines (Italy)

Evaluating the state of activity of Deep-Seated Gravitational Slope Deformation (DSGSD) is a challenge that requires multidisciplinary analytical approaches. This research focuses on the slope-scale gravitational process, framing the role of the Quaternary morphodynamics of a river valley where multiple DSGSDs coexist, to reconstruct the causative factors controlling slope instabilities in a long-term evolutionary history. The study area, located in the Velino River Valley (Rieti, Central Italy) and the San Vittorino intermontane plain, experienced a complex geological history significantly influenced by the interplay of tectonic and climatic processes. The Quaternary geomorphological evolution of this sector was framed to shed light on fluvial and slope dynamics and assess the residual landslide hazard along the valley. In this research, we investigated the case study of the Paterno slope, which, according to the previous official risk mapping, was characterized by a high risk. The reported reconstruction is based on numerous breccia outcrops distributed at different elevations along the slope, leading to an updated evolutionary model of the Velino River and Paterno slope system, which is further corroborated by the most current official risk mapping. This study also allows us to infer the preparatory role of karstic and fluvial processes in Quaternary morphoevolution. Geomorphic markers, such as evidence of flat surfaces and a paleolandscape resulting from erosional processes, have been identified at different sites along the Velino Valley, attributed to the Lower Villafranchian (2.58 Ma). The reported findings revealed that these deposits, composed mainly of slope talus breccias, outcrop at elevations lower than that of the relict ‘Fontanelle Surface’ in the study area since they are partially dislodged by gravitational processes. Geomorphic analysis, together with field investigations and laboratory analyses, focused on these breccias, trying to understand their genesis and Quaternary history. Based on these findings, combined with field surveys, geomorphological analysis and evidence from InSAR satellite data, we revisit the extent and current state of activity of the Paterno DSGSD. As a result, this multidisciplinary approach led us to propose an updated hazard assessment, indicating a low level of associated hazard, also adding pieces of evidence to the morphoevolution of the area with a lookout to the residual risk conditions in this sector of the Apennine mountain chain. This transferable combination of multiple techniques to support the DSGSD hazard assessment can be applied to other mountainous contexts prone to DSGSD. This study aims to provide a comprehensive example of how geomorphological large-scale analysis, integrated with local thin section analysis and remote sensing, can be adopted to make a step in the analysis of DSGSD affecting tectonically active mountain areas.